Ordinarily, Paul Hegness wouldn’t have looked twice at Lot 217 as he strolled through an Irvine auction warehouse, preferring first-edition books and artwork to the box stuffed with old papers and holiday cards.

But then, he wouldn’t have stumbled upon a confession from one of America’s great authors. Inside the box, an envelope postmarked Sept. 12, 1929, caught his eye. It was addressed to John Beardsley, Esq., of Los Angeles. The return address read, “Upton Sinclair, Long Beach….”

The last paragraph got the Newport Beach attorney’s attention. “This letter is for yourself alone,” it read. “Stick it away in your safe, and some time in the far distant future the world may know the real truth about the matter. I am here trying to make plain my own part in the story.”

The story was “Boston,” Sinclair’s 1920s novelized condemnation of the trial and execution of Nicola Sacco and Bartolomeo Vanzetti, Italian immigrants accused of killing two men in the robbery of a Massachusetts shoe factory.

Prosecutors characterized the anarchists as ruthless killers who had used the money to bankroll antigovernment bombings and deserved to die. Sinclair thought the pair were innocent and being railroaded because of their political views.

Soon Sinclair would learn something that filled him with doubt. During his research for “Boston,” Sinclair met with Fred Moore, the men’s attorney, in a Denver motel room. Moore “sent me into a panic,” Sinclair wrote in the typed letter that Hegness found at the auction a decade ago.

“Alone in a hotel room with Fred, I begged him to tell me the full truth,” Sinclair wrote. ” … He then told me that the men were guilty, and he told me in every detail how he had framed a set of alibis for them.”